Optical systems and circuits for data communication, optical recording and computing, optical measuring instruments and medical applications become more and more important. Bandwidths of different optical fibers are used in these systems and circuits. Since optical fibers have the attractive advantage of not only large transmission capacity but lack of electromagnetic interferences and ground loop problems, fiber-optic technologies are almost ideally suited for the previously mentioned technical fields.
For the control and operation of optical fiber networks and other fiber applications different optical switches are necessary for disconnecting fiber links, for switching from one link to another or for multiplexing and demultiplexing. Most of the applications of switches have to be very reliable and should have only low losses.
The following sections relate mainly to fiber optic networks, e.g. LANs (Local Area Network), and switches for the same. In FIG. 1 a typical LAN is schematically shown. This LAN consists of an optical fiber ring 12 to which stations (e.g. PCs, Hosts, Routers, Concentrators) 10.1-10.8 are connected via distribution panels 13.1-13.8. The stations and distribution panels may be connected to one or two optical paths (rings or buses) i.e. by two fibers (single-attach) or four fibers (dual-attach). The distribution panels 13.1-13.9 of the shown application example consist mainly of bypass switches. A detailed sketch of a dual-attach configuration is shown in FIGS. 2A and 2B. The terminal 10.1 is connected via four optical fibers C, D, G, H to the passive distribution panel 13.1. If the terminal 10.1 is unpowered or in self-testing state it is not inserted into the network 12, as illustrated in FIG. 2A. It is in a bypass-and-wrap state. When the terminal 10.1 wants to insert into the network 12, the distribution panel 13.1 switches from bypass to insert state shown in FIG. 2B. This complex switching function can be realized by using four coupled change-over switches. A new and inventive GRIN-rod lens switching element with integrated planar mirror, which will be described below, can be used to realize these switching functions.
Different types of optical switches are known in the art. They are currently built with linear displacement switches where the fibers are pushed from one alignment to another by electro-magnetic or piezo-electric actuators. One example out of a great number of known publications relating to these switches is given by the article "Optical bypass switch for fiber-optic data bus systems", of M. Nunoshita et. al., Appl. Optics, Vol. 19, No. 15, pp. 2574-2577, August 1990. The switch described in this article has an iron piece with a pair of mirrors which can be attracted by a magnetizable electromagnet. In addition to the optical fibers it needs copper lines for the powering of the electromagnet. To realize switching functions similar to that described in context with FIG. 2A and FIG. 2B, two of the electromagnetic switches described in the article of M. Nunoshita are necessary. The combination of two electromagnetic switches is very bulky and needs separate copper lines for powering and control.
The inventive switch is constructed such that there is no need for external copper lines for the powering and control of the switch. It is remotely optically powered via the given fibers. Transmission of power by light is advantageous in most of the applications since there is no need for additional copper lines and since galvanic separation is achieved. The switches according to the present invention can be remotely powered and controlled using the data transmission fibers such that no additional fibers are required. The principle of remote optical powering is described in context with FIG. 3A and FIG. 3B. In these figures, a single-attach distribution panel 30 with fiber inputs/outputs A-D is illustrated. In the power-off and self-test phase, FIG. 3A, of a terminal 35 which is connected via fibers C and D to the distribution panel 30, the terminal 35 is not linked to the LAN 12. During this phase, the terminal 35 cannot receive or send data to the LAN 12. When the station wants to insert into the LAN 12, as illustrated in FIG. 3B, a powering laser diode 31 (PLD) emits a powering signal with wavelength .lambda..sub.p which is coupled into the fiber D via a wavelength-division multiplexer 32 (WDM). Another WDM 33, part of the distribution panel 30, feeds the powering signal to a converter 34 which converts the received powering signal into electric current. A switch being part of the distribution panel 30 is switched from one state to another by said current. In this state, the terminal 35 is linked to the LAN 12 and data signals with wavelength .lambda..sub.s are guided from and to the ring.
To ensure reliable operation of the switch, efficient power transmission and conversion is important. The optically driven power source 34, also called converter, has a limited output power. The power consumption of the actuators of the optical switches have to be adapted to the output power of the power source 34. A special SMA (Shape Memory Alloy) actuator which can be powered by a converter 34 is disclosed in context with one of the embodiments of the present invention.
In addition, a new and inventive GRIN-rod (graded-refractive-index-rod) lens with integrated planar mirror is disclosed hereinafter, which can be used for different applications in optical systems and in particular for switches according to fiber optic networks, e.g. 16 Mb/s-Token Rings or FDDI (Fiber Distributed Data Interface) or DQDB (Distributed Queue Dual Bus). GRIN-rod lenses have a number of features that make them particularly suitable for optical devices and for manipulating and processing signals in optical fiber communication systems. Several applications of GRIN-rod lenses are known in the art. To obtain a general view of GRIN-rods and state-of-the-art in this technical area, the following, chronologically ordered, articles are quoted. An analysis of the aberration of GRIN-rod lenses is published by W. J. Tomlinson in the article "Aberration of GRIN-rod lenses in multimode optical fibers", Appl. Optics, Vol. 19, No. 7, pp. 1117-1126, April 1980. Different designs of GRIN-rod lens devices, including connectors, attenuators, directional couplers, switches, isolators and wavelength-division multiplexers (WDMs) are reviewed by the same author in the publication "Applications of GRIN-rod lenses in optical fiber communication systems", Appl. Optics, Vol. 19, No. 7, pp. 1127-1138, April 1980. One example for a GRIN-rod lens employed in optical measuring instruments is given by the article "Rapid communication, A reflective optical sensing technique employing a GRIN rod lens", of S. D. Cusworth and J. M. Senior, J. Phys. E: Sci. Instrum., Vol. 20, pp. 102-103, 1987.
The nearest prior art to the GRIN-rod lens switching elements with integrated planar mirror, as hereinafter claimed and described, is given by a publication of F. Gfeller, "Bypass switch for optical fiber ring network", IBM Technical Disclosure Bulletin, Vol. 24, No. 3, pp. 1493-1495, August 1981. An optical GRIN-rod switch is described in this article which has to be electrically powered via separate copper lines. Electromagnets are employed for moving two liquids, mercury and a ferrofluid, through the optical path inside a GRIN-rod lens. With the current converted from a photodiode (order of 1 mA), as herein described, an electromagnet can hardly be used to produce a sufficient magnetic field strength to move the ferrofluid. (Relay magnets generally need 50 mA and more). However, these liquids might be moved by a SMA actuator pressing on a diaphragm or piston, but the force needed may well be higher than that provided by the current invention. It appears therefore very unlikely that the fluids can be moved by an SMA actuator with about 1 mW heating power.
The nearest prior art to fiber optic switches is given by a publication of P. Heinzmann and H. R. Mueller "Integrated fiber optical switching element", IBM Technical Disclosure Bulletin, Vol. 32, No. 10B, pp. 172-174, March 1990. In this article, an optical switching element is proposed comprising silicon microfabricated mechanical parts with integrated optical waveguides.
No prior art is known to the inventors relating to remotely optically powered switches and GRIN-rod lenses with integrated planar mirror, as described and claimed hereinafter.